Bottom Line:
Verbal comprehension skills did not diminish during the follow-up, but productive speech deteriorated because of dyspraxia and dysarthria.Thus, the results indicate better prognosis in cognitive skills than earlier assumed.The early neurocognitive development predicts the later course of motor and cognitive development.

Background: Salla disease (SD) is a rare lysosomal storage disorder leading to severe intellectual disability. SD belongs to the Finnish disease heritage, and it is caused by mutations in the SLC17A5 gene. The aim of the study was to investigate the course of neurocognitive features of SD patients in a long-term follow-up.

Methods: Neuropsychological and neurological investigations were carried out on 24 SD patients, aged 16-65 years, 13 years after a similar examination.

Results: The survival analysis showed excess mortality among patients with SD after the age of 30 years. The course of the disease was progressive, but follow-up of SD patients revealed that motor skills improved till the age of 20 years, while mental abilities improved in most patients till 40 years of age. Verbal comprehension skills did not diminish during the follow-up, but productive speech deteriorated because of dyspraxia and dysarthria. Motor deficits were marked. Ataxia was prominent in childhood, but it was replaced by athetotic movements during the teens. Spasticity became more obvious with age especially in severely disabled SD patients.

Conclusions: Younger SD patients performed better in almost every task measuring mental abilities that then seem to remain fairly constant till early sixties. Thus, the results indicate better prognosis in cognitive skills than earlier assumed. There is an apparent decline in motor skills after the age of 20 years. The early neurocognitive development predicts the later course of motor and cognitive development.

Fig2: Rate of change in developmental age during the 13-year follow-up. The rate of change in motor (a) or mental (b) developmental age was calculated per year of follow-up. Data at the baseline visit were obtained from [7]. Values are plotted at the midpoint between the age at baseline and that at the follow-up visit

Mentions:
The median age of the 24 SD patients was 34 years (range, 16–65 years) at the follow-up visit. The rate of change in motor and mental developmental age was calculated for each patient (Fig. 2). Between the baseline study and the follow-up study, the change in motor developmental age (Fig. 2a) was positive till the age of 20 years in most patients, but after that age, motor skills declined. There was no correlation between the rate of change in motor developmental age and the chronological age (Pearson r = −0.395, p = 0.056). There was an increase in mental developmental age in most patients till their late thirties (Fig. 2b), but beyond that, there was no further change. Indeed, there was an inverse correlation between the rate of change in mental developmental age and the chronological age (Pearson r = −0.481, p = 0.017). Finally, there was a correlation between the rate of change in mental developmental age and that in motor developmental age (Pearson r = 0.685, p = 0.0002).Fig. 2

Fig2: Rate of change in developmental age during the 13-year follow-up. The rate of change in motor (a) or mental (b) developmental age was calculated per year of follow-up. Data at the baseline visit were obtained from [7]. Values are plotted at the midpoint between the age at baseline and that at the follow-up visit

Mentions:
The median age of the 24 SD patients was 34 years (range, 16–65 years) at the follow-up visit. The rate of change in motor and mental developmental age was calculated for each patient (Fig. 2). Between the baseline study and the follow-up study, the change in motor developmental age (Fig. 2a) was positive till the age of 20 years in most patients, but after that age, motor skills declined. There was no correlation between the rate of change in motor developmental age and the chronological age (Pearson r = −0.395, p = 0.056). There was an increase in mental developmental age in most patients till their late thirties (Fig. 2b), but beyond that, there was no further change. Indeed, there was an inverse correlation between the rate of change in mental developmental age and the chronological age (Pearson r = −0.481, p = 0.017). Finally, there was a correlation between the rate of change in mental developmental age and that in motor developmental age (Pearson r = 0.685, p = 0.0002).Fig. 2

Bottom Line:
Verbal comprehension skills did not diminish during the follow-up, but productive speech deteriorated because of dyspraxia and dysarthria.Thus, the results indicate better prognosis in cognitive skills than earlier assumed.The early neurocognitive development predicts the later course of motor and cognitive development.

Background: Salla disease (SD) is a rare lysosomal storage disorder leading to severe intellectual disability. SD belongs to the Finnish disease heritage, and it is caused by mutations in the SLC17A5 gene. The aim of the study was to investigate the course of neurocognitive features of SD patients in a long-term follow-up.

Methods: Neuropsychological and neurological investigations were carried out on 24 SD patients, aged 16-65 years, 13 years after a similar examination.

Results: The survival analysis showed excess mortality among patients with SD after the age of 30 years. The course of the disease was progressive, but follow-up of SD patients revealed that motor skills improved till the age of 20 years, while mental abilities improved in most patients till 40 years of age. Verbal comprehension skills did not diminish during the follow-up, but productive speech deteriorated because of dyspraxia and dysarthria. Motor deficits were marked. Ataxia was prominent in childhood, but it was replaced by athetotic movements during the teens. Spasticity became more obvious with age especially in severely disabled SD patients.

Conclusions: Younger SD patients performed better in almost every task measuring mental abilities that then seem to remain fairly constant till early sixties. Thus, the results indicate better prognosis in cognitive skills than earlier assumed. There is an apparent decline in motor skills after the age of 20 years. The early neurocognitive development predicts the later course of motor and cognitive development.